Samoa Guide, 15. Old fish caught locally

Two fisheries in American Samoa currently target coral reef fish -- the subsistence fishery and the artisanal (small-scale commercial) fishery. Subsistence fishing includes the multiple ways that Samoans have always caught nearshore fish for food. In modern times, this includes rod and reel, bamboo pole and line, free-diving, throw nets, gillnets, and gleaning (handpicking clams and octopus). Stone weirs for atule and enu baskets for juvenile goatfish (i’asina) are still used in Manu’a. On Tutuila, subsistence catches appear to be modest in size and have been declining steadily over the past 20 years due to lifestyle changes (more people have regular jobs).

The artisanal fishery that sells reef fish to local stores is a relatively recent development. It is conducted by teams of night divers who use underwater flashlights and spears to catch sleeping fish. In the mid 1990s, many of these divers switched from free-diving to scuba diving, which greatly increased the number of fish they caught. This type of heavy fishing had a significant overfishing impact on our reef fish populations, so the use of scuba gear while spear fishing was banned in the Territory in 2001.

Even though current levels of fishing do not seem excessive, the area of our reefs is rather small and consequently it is easily fished out. Fish stocks may well have been depleted years ago – knowledgeable locals and elder Samoans recall seeing far more fish on our reefs 25 years ago.

A meaningful recovery will require nothing short of a territory-wide reduction in the harvest of coral reef fishes for at least 10 years, with specific protection for the larger fish. That’s what the long life span of the fish is telling us. There is no quick fix. Additionally, setting aside some areas as marine protected areas is an essential component for the recovery of fish stocks. To be effective, such areas must provide long-term protection by being permanently closed to all fishing. Marine protected areas that are periodically opened up to fishing may satisfy short-term goals, but they do not allow the fish to grow big and old, and it is these old-timers that produce the most fish eggs. For example, one large snapper (mu) 24 inches long releases as many eggs as 212 snappers that are 17 inches long.

So, that 18 year old alogo was not just an unusual trophy – it was also a vital member of the fish community that spawned year after year, thereby insuring that some young fish survived to maintain a healthy population of alogo on our reefs.

Every so often however, during years when the ocean currents and conditions are just right, massive numbers of young fish survive and appear on our reefs, like pala'ia (young pone surgeonfish) or i'asina (young goatfish).

While this is all very interesting of course, there is an important takehome message. It is easy to overfish populations with these life history characteristics. Having a long life span and spawning repeatedly may be a successful strategy under natural conditions, but it also makes these fish extra vulnerable to overfishing. That's because fishermen tend to harvest the larger (older) fish in the population. Under heavy fishing pressure, all the old fish may be taken, leaving only the smaller, younger fish. That would put the population in a very precarious situation, because the younger fish left may not yet be old enough to spawn.

That appears to be exactly what has happened in American Samoa because there are relatively few and/or small sizes of the species commonly taken for food left on our reefs. The graph at right shows the pooled lengths of all surgeonfish, unicornfish, parrotfish, snappers, emperors, groupers, jacks and sharks sighted during extensive scientific surveys on the reef slope at the 30-ft depth. Few fish were 16 inches (40 cm) or larger. This depressing picture is not a sudden event – surveys in 1996 and 2004 show similar results.

What's even more astonishing is that an alogo caught in Australia's Great Barrier Reef was 44 years old. I am not kidding. There were also other alogo in the Australian sample that were 20-40 years old, so the record age of 44 is believable. These old fish were not unusually large, just the standard size alogo.

It turns out that this is not unusual for coral reef fish. Recent studies show that several other species of surgeonfish (pone), unicornfish (ume), groupers (gatala) and snappers (mu) can also live up to 20-40 years. These findings are beginning to reshape our understanding about the ecology of coral reef fishes and their vulnerability to overfishing. The occurrence of many long-lived fish in a population indicates that the coral reef fish community is quite stable, with a low replacement of individual fish. Once a young fish gets to the reef, it may be there for decades.

Why would these fish live so long? The answer provides some key information about the environment that the fish live in. Fish typically exhibit this type of life cycle (long life span and repeat spawning) when few of their young survive. That's certainly the case for coral reef fish – their thousands of eggs and larvae drift around with the ocean currents for weeks or months. Very few of them make it back to the reefs. So, if all their young usually die, the adult fish need to live a long time and spawn repeatedly to make sure that at least some young survive. If the adults lived only a short time, the population might disappear altogether.

This is hard to believe -- an 18 year old alogo was caught in American Samoa. That's old enough to get a drivers license.

We're talking about the alogo, also known as the blue-lined surgeonfish Acanthurus lineatus. Nothing unusual about its size -- it was the typical 8-inch alogo you see in the stores. And I ate it. All that remained were the little bones that scientists use to determine the age of the fish. These bones, when looked at under a microscope, have concentric circles, one for each year, just like tree rings. You just count the rings and that's how old the fish is.